This invention is generally directed to the use of new hole transporting compositions, and more specifically the present invention is directed to improved photoresponsive imaging members containing as hole transporting substances certain known polysilylene compositions. In one important embodiment of the present invention, there is provided a layered photoresponsive imaging member comprised of a polysilylenes hole transporting compound, and a photogenerating layer. Further, there is provided in one particular aspect of the present invention an improved layered photoresponsive imaging member comprised of a supporting substrate, a photogenerating layer, and in contact therewith a hole transport layer comprised of a polysilylene compound, especially poly(methylphenylsilylene), poly(m-propylmethylsilylene), and other similar silylenes. The layer with the polysilylenes hole transporting compound can be located as the top layer of the imaging member, or alternatively it may be situated between the supporting substrate and the photogenerating layer. Moreover, the present invention relates to the use of the improved imaging members disclosed in electrophotographic, and especially xerographic, imaging processes.
The formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known, one such method involving the formation of an electrostatic latent image on the surface of a photosensitive plate, referred to in the art as a photoreceptor. The photoreceptor may comprise a conductive substrate containing on its surface a layer, or layers, of photoconductive insulating materials, and in many instances, there can be used a thin barrier layer between the substrate and the photoconductive layer to prevent charge injection from the substrate into the photoconductive layer upon charging of its surface, since charge injection would adversely affect the quality of the resulting image.
Numerous different photoconductive members for use in xerography are known, including, for example, a homogeneous layer of a single material such as vitreous selenium, or composite layered imaging members, with a photoconductive compound, dispersed in other substances. An example of one type of composite photoconductive layer used in xerography is described for example, in U.S. Pat. No. 3,121,006, wherein there is disclosed a number of layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In a commercial form, the binder layer contains particles of zinc oxide uniformly dispersed in a resin binder and coated on a paper backing. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result the photoconductive particles must be in a substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, with the uniform dispersion of photoconductive particles described a relatively high volume concentration of photoconductor material, about 50 percent by volume, is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. These high photoconductive loadings can result in destroying the physical continuity of the resin thus significantly reducing the mechanical properties of the binder layer. Illustrative examples of specific binder materials disclosed in this patent include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor materials comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain higher quality images. The photoconductive imaging member of the present invention represents such an improved member, and has other advantages as disclosed hereinafter.
Recently, there has been developed layered photoresponsive imaging members, including those comprised of generating layers and transport layers as disclosed in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials with a hole injecting layer, overcoated with a transport layer, followed by an overcoating of a photogenerating layer and a top coating of an insulating organic resin, reference U.S. Pat. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium and metal, or metal free phthalocyanines, while examples of the transport compounds that may be employed are comprised of certain aromatic amines as mentioned herein. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990 and 4,251,612 are totally incorporated herein by reference. The U.S. Pat. No. 4,265,990 is of particular interest in that it discloses layered photoresponsive imaging members similar to those illustrated in the present application with the exception that the hole transporting substances of this patent are comprised of aryl amine compositions, while in accordance with the present invention the hole transporting substance is a polysilylene.
Many other patents are in existence describing photoresponsive imaging members including layered imaging members with generating substances such as U.S. Pat. No. 3,041,167, which describes an electrophotographic imaging member with an overcoated imaging member containing a conductive substrate, a photoconductive insulating layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging the member with an electrostatic charge of a first polarity, and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity, which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer such as by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image is present across the photoconductive layer and the overcoating layer.
There is also disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting the photogenerated hole into a continuous active layer containing a transport organic material which is substantially non-absorbing in the spectral region of intended use, but which is active and allows injection of photogenerating holes from the photoconductive layer and provides for these holes to be transported through the active layer. The active compounds may be mixed with inactive polymers or non-polymeric materials.
In U.S. Pat. No. 3,041,116 there is disclosed a photoconductive material with a transparent plastic material overcoated on a layer of vitreous selenium, which is present on a recording substrate. Apparently, in operation, the free surface of the transparent plastic is electrostatically charged to a desired polarity, followed by exposing the imaging member to activating radiation, which generates a hole electron pair in the photoconductive layer and wherein the electrons move to the plastic layer and neutralize the positive charges contained on the free surface of the plastic layer, thus creating an electrostatic image. Also, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383 the use of sodium carbonate doped and barium carbonate doped photoresponsive imaging members containing trigonal selenium. Other representative patents disclosing layered photoreponsive imaging members include U.S. Pat. Nos. 4,115,116, 4,047,949 and 4,081,274.
While imaging members various hole transporting substances, including aryl amines are suitable for their intended purposes, there continues to be a need for the development of improved members, particular layered members, which are comprised of new hole transporting substances. Moreover there continues to be a need for specific layered imaging members which not only generate acceptable images, but which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Additionally, there continues to be a need for improved layered imaging members wherein the materials employed for the respective layers, particularly the hole transporting layer, are substantially inert to the users of these members. Further, there continues to be a need for improved photoresponsive imaging members which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of these imaging members in repetitive imaging processes. Also, there continues to be a need for new hole transporting compounds that are also useful as protective overcoating layers, and as interface materials for various imaging members. Furthermore, the hole transporting polysilylenes compositions of the present invention may be useful as binder polymers for photogenerating substances comprised of organic materials. There also is a need for new hole transporting substances which enable increased mobility of holes in layered imaging members. Likewise, there is a need for hole transporting compounds with increased stability, for example wherein there is no extraction of these compounds from the layered imaging members in which they are incorporated, when for instance liquid developers are selected for rendering the latent electrostatic latent image visible. Furthermore, there is a need for hole transporting compounds useful in layered imaging members, which compounds are superior insulators in the dark, compared to many other known hole transporting compounds, thus enabling charging of the resulting imaging member to higher fields, while maintaining cyclic stability, and allowing improved developabilty. Also, there is a need for imaging members with new hole transporting compounds, which can function as resinous binders. Additionally, there is a need for enabling the preparation of imaging members with new hole transporting compounds, wherein the preparation allows for the selection of a variety of solvents, inclusive of toluene, benzene, tetrahydrofuran, cyclohexane, and halogenated solvents, in addition to methylene chloride.